The present invention relates to a multistage centrifugal compressor used in petrochemistry plants and process equipment of general industry, and more particularly to a centrifugal impeller constituting each stage of such multistage centrifugal compressor and a method for producing the same.
The impeller used in the multistage centrifugal compressor comprises two rotary discs (a disk and a shroud), and a plurality of vanes disposed between the disk and the shroud and substantially equidistantly in a circumferential direction to define passages by means of the disk and the shroud and the vanes. The disk, the shroud and the vanes are so designed and manufactured as to provide a proper velocity distribution of a working gas for every stage.
Further, the suction temperature and the suction pressure of the impeller vary for each stage because the fluid to be employed is a gas with compressibility.
As a result, the density of the gas varies in the stages, and the desired width of the gas passage of the impeller, that is, the vane height, is made narrower as going downstream(a suction port, a first stage, a second stage, . . . ), and therefore the impellers of the respective stages need to be different in configuration from each other.
Consequently, the multistage centrifugal compressor is heretofore produced in such a manner that a suitable configuration of the impeller has been decided for every stage and the disk and the shroud have been manufactured separately by machining in accordance with the decided configuration of the disk and the shroud of the impeller of each stage. The vanes have been shaped into the required configuration by press working and integrated into the disk and the shroud by means of welding or the like.
Meanwhile, there has been employed another method in which a simple shape of a vane, such as a two-dimensional vane, is substituted for the optimum shape of the vane for every stage, and then such simple shaped vane is made by casting or the like. Moreover, there has been known still another method in which a multispindle NC machine tool is used to make the vane of a complicated shape for a half-shrouded impeller with no shroud.
In the various methods described above, it is necessary that the impellers of the respective stages are so designed and manufactured as to be different in configuration from each other. These methods for producing an impeller for centrifugal compressor are disclosed in Japanese Patent Unexamined Publication Nos. 2-161200 and 3-151597.
In the former, a shroud is made axially movable for the purpose of suppressing occurrence of surging to obtain a high-efficiency impeller. However, there is given no consideration for the reduction of the number of manufacturing steps in producing the impeller, such as employment of a process of the impeller common to a plurality of stages.
On the other hand, in the latter, the width of the passage at an outlet of the impeller is adjustable for the purpose of regulating the flow rate to enhance the efficiency. However, there is also given no consideration for the reduction of the number of manufacturing steps, such as employment of a process and a design common to a plurality of impellers.
According to both of these conventional technologies, the impeller has been designed and manufactured for every stage, and no consideration has been given for the reduction of the number of required processing steps in order to manufacture an impeller for a centrifugal compressor at low cost.
It is an object of the present invention to provide an inexpensive multistage centrifugal compressor, an inexpensive impeller for a multistage centrifugal compressor and a method for producing an inexpensive impeller, without the above-described problems of the prior art.
It is another object of the invention to employ a production process of the impeller common to the stages of the multistage centrifugal, in which the impellers had to be conventionally designed and manufactured individually for the respective stages due to the compressibility of a gas.
It is still another object of the invention to be able to employ a common NC program or a common pressing die which is to be used in manufacturing the impeller for a multistage centrifugal compressor.
It is a further object of the invention to provide a high-efficiency multistage centrifugal compressor free from the reduction in performance of the multistage centrifugal compressor, a high-efficiency impeller for a centrifugal compressor and a method for producing such a high-efficiency impeller, while achieving the above objects.
It is a still further object of the invention to provide a high-reliability impeller for multistage centrifugal compressor and a method for producing the same by simplifying the production process.
To these ends, according to one aspect of the present invention, there is provided a multistage centrifugal compressor comprising: a plurality of impellers mounted on a rotary shaft apart from one another, each of the impellers including a disk, a shroud and a plurality of vanes disposed between the disk and the shroud and separated from one another in a circumferential direction; and a casing for housing these impellers, the casing being formed with a suction port and a discharge port, a gas drawn into through the suction port being compressed in sequence by the rotation of the impeller of every stage and discharged from the discharge port, wherein a whole of the vane of one of at least two impellers has a configuration identical to a part of the vane of the other impeller.
Preferably the one impeller is provided in a stage more remote from the suction port of the multistage centrifugal compressor than the other impeller is.
It is also preferable that the one impeller is provided in a stage disposed downstream of the gas flow in the multistage centrifugal compressor than the other impeller is.
According to another aspect of the present invention, there is also provided a multistage centrifugal compressor in which centrifugal compressors are connected in multiple stages through piping, each of which comprises: a rotary shaft; an impeller including a disk fixed to the rotary shaft, a shroud fixed to the rotary shaft, and a plurality of vanes disposed between the disk and the shroud and separated from one another in a circumferential direction; and a casing housing the impeller and having a suction port through which a gas is drawn in and a discharge port from which the compressed gas is discharged, wherein the vane of one of the impellers of at least two stages of centrifugal compressors has a configuration identical with a part of a vane of the other of the impellers of at least two stages.
Preferably an intercooler is disposed between the respective stages of centrifugal compressors.
It is preferred that the one impeller is disposed downstream of the other impeller with respect to a gas passage formed within the multistage centrifugal compressor made up of the connected centrifugal compressors.
In still another aspect of the invention, a centrifugal impeller is used in either of the above-described multistage centrifugal compressors.
Further, there is provided an impeller for a multistage centrifugal compressor comprising: a disk; a shroud; and a plurality of vanes disposed between the disk and the shroud and separated from one another in a circumferential direction, wherein the vane is made up of a group of linear line segments each extending from a disk-side edge to a shroud-side edge, the linear line segments of the group being changed in length individually. Further, the corresponding two linear line segments of adjacent impellers are different in length from each other so as to form different vanes for plural stages of the multistage centrifugal compressor.
It is preferred that an NC machine tool is used to manufacture this kind of vane.
In another aspect of the invention, there is provided a method for producing an impeller for a multistage centrifugal compressor comprising a disk, a shroud and a plurality of vanes disposed between the disk and the shroud and separated from one another in a circumferential direction, the method comprising the steps of: preparing a plurality of sets of flat vane blanks, the flat vane blanks in one set formed in a meridional cross-section surface shape different from the flat vane blanks in another set; pressing these blanks by means of the same press dies to form the vanes of different configurations; and attaching the vanes of each of the sets to the disk and the shroud to produce impellers for different stages, respectively.
According to the present invention, the vanes constituting the different impellers of the multistage centrifugal compressor can be formed by partially cutting off and press forming the same vane blanks. Namely, only a single kind of vane blank (master vane blank) is needed for the different vanes. More specifically, the vanes comprise three-dimensional complicatedly-undulating surfaces. The vane which is formed by press forming a whole master vane blank is used in an impeller for a first stage. The vane which is formed by press forming a master vane blank partially cut off (or almost the whole master vane blank) is used in an impeller for a second stage. The vane which is formed by press forming a master vane blank further partially cut off (or a substantial part of the master vane blank) is used in an impeller for a third stage. Namely, in an impeller for a later stage, a smaller part of the master vane blank is used to form a vane. Accordingly, only by putting between two press dies the vane blank which is defined by partially cutting the master vane blank off and has an area required for the vane of the impeller of the stage, the vanes of every stage can be easily produced.
Meanwhile, in case of production by an NC machine, it is necessary to change only the coordinates of the shroud wall surface and the disk wall surface. The coordinates between the shroud and the disk are common to every stage, and therefore the program can be used in common.
Further, it is not always necessary that the master vane blank is used for all the stages. The master vane blank may be changed every two stages, for example a first master vane blank for the first and the second stages and a second master vane blank for the third and the fourth stages. Also the master vane blank may be used merely for the first and the second stages and different vane blanks may be used for the respective stages other than the first and the second stages.